Characterization of nano-magnetic structures

Since many important magnetic properties are affected (and thus can be manipulated) by microstructural features, it is important to characterize the physical and magnetic structures at the highest resolutions. Unfortunately, the resolution of electron microscopes is optimized for a given wavelength by high field lenses (similar to 1-2 tesla), which can easily saturate the specimen. Thus, to obtain high resolution structural and magnetic information in the same instrument is not possible, unless it is specially designed or sufficiently flexible. An example of the latter is the improved magnetic resolution obtained on the 800 kV Berkeley ARM and its applications to domains in Co-X binary alloys. Much of the restriction on high resolution revolves around specimens very thin in the beam direction (less than or equal to 200 Angstrom) and the signal-to-noise problem. Even with high resolution, sufficient image contrast is necessary to define the mesostructure. This paper discusses some of these issues, together with the problem of identification of atomic species, and effects associated with interfaces. Examples are drawn from current work on hard magnets, oxides and GMR in alloys. (C) 1997 Acta Metallurgica Inc.